Phase shifter having different length conductors inserted into circuit by reed relays



Oct. 7, 1969 R. A. FELSENHELD TA!- 3,471,308

PHASE SHIFTER HAVING DIFFERENT LENGTH CONDUCTQRS INSERTED INTO CIRCUITBY REED RELAYS Filed June 9. 1966 INYENTORS.

ROBEk? A. false/V0540 BY MURRAY HOFFMAN EMMA/Vl/El J. we

AGENT 5 United States Patent PHASE SHIFTER HAVING DIFFERENT LENGTHCONDUCTDRS INSERTED INTO CIRCUIT BY REED RELAYS Robert A. Felsenheld andMurray Hofiman, Livingston, and Emmanuel J. Perrotti, Ramsey, N..l.,assignors to International Telephone and Telegraph Corporation, Nutley,N.I., a corporation of Maryland Filed June 9, 1966, Ser. No. 556,342int. Cl. H03h 7/30 US. Cl. 333-31 1 Claim ABSTRACT OF THE DISCLOSUREThis invention relates to phase shifters and the main object is toprovide a novel, economical phase shifter operable over a wide band offrequencies utilizing switching means for inserting selected lengths ofconductors in the transmission path of a signal to provide a phaseshift.

According to the invention a phase shifter is provided which comprises aplurality of conductors, at least some of which are of differentlengths, each of said conductors being coupled to a source of signalsand to means for receiving signals via switches and means forcontrolling the switches, the distance between said source of signalsand each inoperative switch associated therewith, and the distancebetween said means for receiving signals and each inoperative switchassociated therewith being multiples of a half wavelength at thefrequency of operation, so that an unselected conductor appearssubstantially as a true open circuit.

The above mentioned and other objects of this invention will becomeapparent by reference to the following description taken in conjunctionwith the accompanying drawings in which:

FIGURE 1 is an illustration of a preferred embodiment of this invention;and

FIGURE 2 is a section view of the configuration illustrated in FIGURE 1.

Referring to FIGURE 1, a preferred embodiment of a phase shifteraccording to this invention comprises input connector 1 coupled to ahigh frequency impedance matching device which comprises member 2 andarms 3 and 4. This type of impedance matching device is well known inthe art and therefore, no further discussion of the operation thereof isdeemed necessary for a proper understanding of the invention hereindescribed. Coupled to arm 3 of matching device 5 is the seriescombination of reed relay 6, conductor 8 and reed relay 7. Conductor 8provides a predetermined phase shift at a particular frequency, whichphase shift is determined by the physical length of conductor 8. Thefree end of relay 7 is coupled to arm 13 of coupling means 17, which inthis embodiment is also an impedance matching device. Impedance matchingdevice 17 comprises member 14 and arms 12, 13, 15 and 16 and operates inthe same well known manner as matching device 5. Coupled to arm 4 ofmatching device 5 is the series combination of reed relay 10, conductor11 and reed relay 9, the free end of reed relay 9 being coupled to arm12 of impedance matching device 17. Con- 3,471,808 Patented Oct. 7, 1969"ice pled to arm 15 of matching device 17 is the series combination ofreed relay 18, conductor 20 and reed relay 19, the free end of reedrelay 19 being coupled to arm 24 of impedance matching device 27.Coupled to arm 16 of matching device 17 is the series combination ofreed relay 21, conductor 23 and reed relay 22, the free end of reedrelay 22 being coupled to arm 25 of matching device 27. Coupled tomember 26 of matching device 27 is an output connector 28.

The above described configuration is mounted on a metallic surface 29,which surface provides a ground plane for the phase shifter. Mounted onthe other side of the delay line configuration is metallic surface 30,as shown in FIGURE 2. This surface 30 is not shown in FIGURE 1 for easeof illustration. Electromagnets 32, 33, 34, 35, 36, 37, 38 and 39 aremounted behind the reed relays and preferably behind surface 29 forselectively actuating the reed relays, thereby closing a transmissionpath from the input to the output. Relay operating means 40 is coupledto the electromagnets for selectively operating same in accordance withthe desired phase shift. Means 40 may be any well known actuating devicefor electromagnets, a limitation :being that only one of the parallelconnected conductors may be inserted in the signal path at any one time.

Members 31 are provided in the structure illustrated in FIGURE 1 asspacers for preventing the ground plane surfaces 29 and 30 fromelectrically shorting out the transmission sections of the phaseshifter. These spacers 31 may be made from any suitable low lossinsulating material at the operating frequencies of the phase shifter.

The lengths of conductors 8, 1'1, 20 and 23 are all different and eachwill provide a different phase shift to a signal being transmittedtherethrough. Therefore, in order to provide a desired phase shift, oneof the two parallel paths in each section of the phase shifter shown inFIG- URE 1 is closed by relay operating means 40 turning on the properelectromagnets which in turn operate the corresponding reed relays. Forexample, if reed relays 6, 7, 18 and 19 are closed by energizingelectromagnets 32, 33, 36 and 37 a predetermined phase shift determinedby the length of the signal path via conductors 8 and 20 will beprovided. Alternatively a path comprising reed relays 6, 7, 21 and 22may be provided by energizing electromagnets 32, 33, 38 and 39, therebyproviding a phase shift which is determined by the physical length ofthe signal path via conductors 8 and 23. Since all of the paths aresubstantially identical except for the conductors of different length,various different combinations of relative phase shifts may be providedby selecting various combinations of signal paths. Note that only one ofthe parallel coupled paths may be closed at a time. If more than onepath in each group of parallel paths is closed, then distortion of thesignal will result. This is because each path provides a different phaseshift and if the signals from the two paths are combined at a junctionpoint (i.e. at the matching device 17) phase distortion of the signalwill result. Furthermore, a mismatch will be produced by the closing oftwo parallel paths, thereby providing additional distortion in amplitudeand phase.

Impedance matching devices 5 and 27 are for properly matching theimpedance of the phase shifter to the impedance of the input and outpututilization devices. For example, assume that the input and outputdevices interfacing the phase shifter each have an impedance of 50 ohmsand that a delay path comprising two reed relays and a length ofconductor have a characteristic impedance of 126 ohms. Then withreference to matching device 5, the combination of member 2 and arm 3 isdesigned to comprise a 50 ohm to 126 ohm transformer in a manner wellknown in the Likewise, member 2 and arm 4 are designed to comprise a 50ohm to 126 ohm transformer.

The same impedance matching transformation is provided 7 by matchingdevice 27.

Matching device 17 provides a 126 ohm to 126 ohm impedance match betweenany two of its arms 12, 13, or 16. Actually, the impedance match betweentwo arms of device 17 is 126 ohm to 50 ohms (at member 14) and back to126 ohms. Matching device 17 may be omitted from the design, butincluding it greatly facilitates initial calibration of the phaseshifter. For example, the exact delay provided by each delay path may beeasily measured by replacing an intermediate coupling point (such asmatching device 17) with another matching device such as device 27coupled to an output means. After these paths (between the input 1 andthe newly inserted matching device) have been calibrated theintermediate matching device 17 is placed back into the phase shifterconfiguration without upsetting the calibration. This is because device17 looks the same electrically as device 27 when it is coupled to adelay path. In a similar manner each delay path may be independentlymeasured and calibrated. Phis enables one to use as many sections asdesired in order to provide the desired magnitude of phase shift whileproviding a fairly simple and very accurate method of calibrating thephase shifter.

In the particular design described herein two reed relays (e.g. relays 6and 7) are connected in series with each length of conductor (e.g.,conductor 8) in order to provide a delay path having a higher impedancewhen the relays are inoperative, thereby providing better isolationbetween the various selectiable signal paths. In order to provide a highisolation between selected paths and non-selected paths, the system isdesigned such that each unselected path looks like a one-half wavelengthstub (or a multiple thereof) at the operating frequency of the phaseshifter. For example, referring to the path co-rnprising arm 3, relay 6,conductor 8, relay 7 and arm 13 (illustrated in FIGURE 1), the distancefrom the electrical center of element 2 to the end of contact 41 ofrelay 6 is designed to look like a one-half wavelength stub (or amultiple thereof) at the operating frequency when relay 6 isinoperative. Likewise, the distance from the electrical center ofelement 14 to the end of contact 44 of relay 7 is also designed to looklike a one-half wavelength stub or a multiple thereof. In order tomaximize the isolation, the length of the path between the free end ofcontact 42 of relay 6 and the free end of contact 43 of relay 7 isdesigned so as not to be a multiple of one-half wavelengths at thefrequency of operation. Preferably the length of the path between freeends of contacts 42 and 43 should be as close as possible to multiplesof onequarter wavelength. Ordinary telephone-type reed relays areutilized in order to keep the cost of the system as low as possiblewhile providing a system capable of operating at powers greatlyexceeding those realizable with diode switches as shown in the priorart.

The phase shifter herein described has an advantage in that it isoperable over a relatively large band of frequencies withoutnecessitating a redesign. The limiting factor is the impedance matchingdevices 5, 17 and 27 which can be designed to provide proper impedancematching over a relatively large band of frequencies.

It should be clear that the above-described embodiment of this inventionmay be expanded by adding more parallel paths per section and/or bycoupling more of the parallel coupled paths in series. Modificationsalong these lines are dictated by the values of phase shift that onewishes to provide, and such modifications may be easily carried outwithin the spirit of this invention by one ordinarily skilled in theart. It is obvious that the more alternate signal paths via differentlength conductors that are provided, the more flexible will be the rangeof possible phase shifts.

It should also be pointed [out at this point that reed relays were usedin this embodiment merely by way of example and that any other types ofswitching devices may be utilized with comparable results.

- While we have described above the principles of our invention inconnection with specific apparatus it is to be clearly understood thatthis description is made by way of example and not as a limitation tothe scope of our invention as set forth in the accompanying claim.

We claim:

1. A phase shifter circuit comprising:

a plurality of conductors, at least some of said conductors being ofdiflerent lengths, for providing a predetermined phase shift at apredetermined frequency; source of signals including impedance matchingmeans; I a signal receiving means including impedance matching means; 7a plurality 10f pairs of normally inoperative reed relays,

one relay of each pair connected between one end of each of saidconductors and said source of signals, and the second relay of each pairconnected between the opposite end of each of said conductors and saidsignal receiving means; and

a control means for energizing a selected pair of said plurality ofrelays so as to insert a selected one of said plurality of conductorsinto said circuit, the balance of the relays remaining inoperative,

wherein the distance between said signal source and each of theinoperative relays directly coupled thereto, and the distance betweenthe signal receiving means and each of the inoperative switches directlycoupled thereto, are multiples of a half wavelength at the frequency ofoperation, so that an unselected conductor appears substantially as atrue open circuit;

and

wherein the distance between any pair of switches coupled via one ofsaid plurality of conductors is a multiple of a quarter wavelength so asto maximize the isolation between the selected and unselectedconductors.

References Cited UNITED STATES PATENTS 2,877,427 3/ 1959 Butler.3,131,367 4/1964 Pitts et a1. 333-31 3,295,138 12/ 1966 Nelson 343854HERMAN K. SAALBACH, Primary Examiner P. L. GENSLER, Assistant ExaminerUS. Cl. X. R. 333-7

